"It's okay, he just called me to say he'd be late and that I should go in and wait for him," Jim replied in his best English accent, fidgeting shyly with his watch.

"Ah, I see – well, you'd better go up then," she replied, and Jim walked passed her and started to climb up the stairs.

He couldn't help smiling as he entered the flat and let the door click shut behind him. This was far, far too easy. He made sure to walk slowly and softly along the hallway - it wouldn't do to make too much noise and attract attention to himself, he was only supposed to be waiting for a friend. It always amazed him just how well the Jim-from-IT disguise worked. Maybe people just couldn't say no to a shy, unassuming geek, or maybe they were just too trusting of strangers. Whichever it was, "Mr Space Invaders pyjamas" was the best disguise he'd ever had.

He stopped just inside the doorway to look around, taking in his surroundings. 'Messy… I like it.' He moved further into the room and turned round, at which point he spotted the experiments littering the kitchen. 'Just like I imagined…' After turning his nose up at one or two of the more unpleasant samples, he walked through to the bathroom and took off his rucksack.

The bath, he noted, was slightly longer than average. This pleased him, as there was nothing worse than not being comfortable in the bath. He put the plug in and turned on the hot water, before beginning to undress. Peeling off the skintight grey t-shirt he'd chosen specifically for his little game with Sherlock, he let it fall to the floor beside him. 'Playing Jim from IT.' Next came his shoes and socks, followed by his trousers. 'Playing gay…' Ah yes, the underwear. Jim had known that would get Sherlock's attention. He could feel himself becoming aroused at the thought of Sherlock watching him so closely. Yes, the underwear could stay on.

He discarded his watch, then opened his bag, putting the contents out on the counter. Black socks, £5, Burton. 'Functional,' he thought as pulled them on. White shirt, £25, Topman. 'Comfortable.' He buttoned it up quickly, leaving the top two buttons unfastened and the collar sticking up. Trousers, £35, H&M. 'Reliable,' he mused as he pulled them up and tucked his shirt in. He'd bought them several years ago and they were still in great condition. Jim moved to close the door – but not lock it – then picked up the black tie he'd left on the counter. As he tied it, he grinned, then he checked his appearance in the mirror above the sink. His cheeks were flushed and his lips were pink; his hair was sticking up slightly and his collar was exactly where he'd left it. 'Fuck… even I'd do me…' he thought with a smirk, then he turned his attention to the bath.

With the tap off, Jim climbed in and lay down, settling himself to one end with his head leaning back onto the edge. He was uncomfortably hard now, turned on by his preparations and the feeling of the hot water against his skin. He closed his eyes and took a moment to relax, though none of the tension had a chance to escape as his thoughts turned to Sherlock once again. The man was perfection.

Tall, slim but strong, with striking blue eyes and a mouth that could only have looked better with Jim's cock in it.

He reached a hand down inside his trousers and began to touch himself through the soft fabric of the expensive underwear.

That long, beautiful, pale neck that really needed Jim's teeth sinking into it to make it look complete.

He unbuttoned the trousers and pulled down the zip to give himself more space.

Those long, graceful legs leading up to that perfectly rounded arse which Jim so desperately wanted to bury himself in.

He pulled the underwear down and began to stroke himself steadily and firmly, moaning softly as he did so.

It would start slowly at first, moving in and out of the detective on all fours in front of him just fast enough to tease.

He kept a steady pace, knowing how close he'd been before he even began.

Sherlock would be reluctant at first, almost unwilling, but soon he'd start to push back against Jim, meeting each movement.

Jim closed his eyes again and leaned his head back further, moaning a little louder this time.

He would speed up and thrust harder, letting Sherlock change the angle of his hips until he was groaning and begging for Jim go harder, faster, more.

He was speeding up, the image in his head so vivid that he could barely control himself. He'd imagined this before, the fantasy, but he'd never tried it out in such an… interesting situation. The hot water and the suit made it all so much better.

He'd move harder, until Sherlock practically screaming for more, until he begged for Jim to touch him and of course, Jim would oblige.

Breathing raggedly as his movements became harder and faster, Jim's hand moved somewhat erratically.

He'd keep going like this, hot and messy, until Sherlock came and clenched tightly around him, and then…

Tightening his grip, it took only a few more strokes before Jim came hard, clinging to the edge of the bath with his free hand and arching his back as he moaned Sherlock's name loudly.

It took some time for him to get his breath back, during which time he pulled the plug out with his toes. It was only when he shivered slightly that he realised how much of the water had drained away. Reluctantly, he got to his feet as he fastened up his trousers again, then he climbed out of the bath. It took only a moment to put everything back into his bag, then he was out of the room, down the stairs and out the front door into the street.

The water would dry before Sherlock got back – Jim had made sure he'd be busy for a while. Jim, on the other hand, was in central London in a cheap suit, soaked to the skin, his face still flushed with arousal. With another smirk, he started to walk towards home, but he stopped to cast one glance back at the flat.

One day, he hoped, he wouldn't need to imagine fucking Sherlock Holmes. For now, he could just find new, exciting and dangerous ways to pretend.

The bath thing had definitely been his favourite so far, he'd have to try that one again.